In web handling processes, wherein a web of flexible material such as a fabric, paper, or metal is continuously passed partly around a guide roll either fixed or rotatably supported on a shaft, it is known to support one or both ends of the shaft by a transducer device capable of measuring the transverse or radial forces exerted on the roll by the tensions in the moving web and then making continuing adjustments to the web tension, responsive to the ongoing web tension measurements, either by manual or automatic control equipment. These known web tension measuring devices customarily include a sensor in the form of a strain beam cantilever mounted on a fixed frame and the flexurable free end of which is coupled to and supports an end of the guide roll shaft through either a thin flexurable steel diaphragm or a pivotal connection such as a self-aligning bearing. Strain gauges are attached to the strain beam and are connected in an electrical circuit to generate a continuous electrical signal. The generated electrical signal caused by the beam deflection due to the web tension forces on the beam are representative of the instantaneous tension in the moving web. Many of these measurement devices are quite sensitive to small force variations, so much so, in fact, that the response curve has an undesirable hysteresis loop therein. This hysteresis was, in part, caused by the friction in the hinged or jointed connection between the axle and the movable, face plate. Thus, as tension on the web increases, the beam bends, resulting in its extended axis, diverging relative to the roller axis, which divergence is taken up by the hinged connection. Undesirable friction in this connection produces a force couple which, as web tension increases, acts to resist the bending of the beam and therefore causes a reduction in the stress applied to the strain gauge and the resultant tension signal. As tension in the web decreases and the beam is unloaded, the friction couple in the hinged connection produces a force couple which acts in the opposite direction and causes an increase in the resultant tension signal. The difference in these signals results in a hysteresis loop in the response curve which makes the sensor unsatisfactory for extremely critical applications.
To overcome these problems, a sensor was introduced which comprised of a pair of parallel spaced arms or beams each integrally connected at one end to the base plate and at the other end to the face plate, which face plate then was connected to the axle of the web roller. As this twin beam sensor was loaded, the extended axis from the face plate remained parallel to the unloaded axis and no force couple was introduced due to the bending of the beams. Accordingly, it was found possible to eliminate the expensive bearing connection and a rigid connection between the shaft and the sensor. Such devices were an improvement, even though, in some instances, a hysteresis loop remained. However, it was found that, particularly when the web roller had a substantial length, the axle of the roller was bent or deflected throughout its length by the web tension forces such that its extended axis was no longer parallel to the extended axis of the face plate. This placed one of the beams in longitudinal tension and the other in longitudinal compression which forces affected the strain gauges in the same manner as bending forces and gave inaccurate results and hysteresis in the response curve. Further, the arrangement had difficulty accommodating these misalignments of the shaft and/or expansions or contractions thereof. Coupling arrangements for the shaft which are disclosed in U.S. Pat. Nos. 4,326,424, 4,674,341 and 4,796,474 to Koenig overcome many of these problems. Although these web tension sensor devices have significantly simplified the fabrication and construction of such devices and have substantially reduced the problems associated with hysteresis, shaft expansion, and roller misalignment, these devices all suffer from shaft mount problems, complex wiring configurations, and are difficult to properly align the transducer to the, forces being applied to the shaft.
Transducer devices which are used to measure large tension forces being applied to a web roller are modified to increase the rigidity of the transducer components. Generally, the flexure beam arrangement includes thicker and heavier components to accommodate the large forces. The transducer also typically includes one or more stop pins to prevent damage to the flexure beam components. The increased weight of these components can adversely affect the resonance frequency of the transducer thereby causing inaccurate readings. The use of stop pins in the transducer increases the complexity of operation, limits the range of operation, and increases the cost of the transducer.